Fluid displacement stimulation of deviated wellbores using a temporary conduit

ABSTRACT

A method of improving the flow of fluids into or along a deviated wellbore that has a partial or complete obstruction caused by fill particles, comprising removing the fill particles from the obstruction and depositing the fill particles within the wellbore, uphole and/or downhole of the partial or complete obstruction. The method described herein removes obstructions and/or stimulates a well in which productivity has been impaired by the presence of fill in the wellbore. This is accomplished without removing the fill from the wellbore, and therefore avoids the consequent disposal or storage considerations.

FIELD

The subject matter disclosed herein relates to a method of stimulating a well, such as a water- or hydrocarbon-producing well.

BACKGROUND

Fluids such as water, oil and gas are collected by wells when the fluids flow from the perimeter of a source rock into the wellbore, and are then removed from the wellbore. Sometimes however, either before or after the well has started production, the rate of recovery of fluids from the wellbore is below that expected. This decreased rate of recovery may be caused by depletion of the reservoir, however it is often caused by a reduction in the porosity and/or permeability of a wellbore, but may also be caused by the obstruction of wellbores by solids, such as sand, silt, and other debris (“fill”). These solids can result in a tortuous flowpath through the cylindrical borehole, which can increase the surface pressure required to inject fluids into a wellbore or reduce the ability of fluids to flow through the wellbore. In some cases fill buildup can result in the wellbore opening becoming completely obstructed, in which case flow is blocked completely.

When the rate of flow of fluids into a wellbore is inadequate, the wellbore may be stimulated to increase its productivity. Stimulation treatment provides the fluids in a source rock with better access into, and/or out of, the wellbore. Various methods have been developed to stimulate wells. One common method of stimulating a well prior to it being put into production is acidizing the well through the use of a “stimulation fluid”.

Hydraulic fracturing is another method of stimulating a well. In this method, a high-pressure fluid (usually water) is injected into a wellbore in order to create fractures or enlarge natural fractures in the formation that allow fluids to flow into the wellbore. Fracture-acidizing is a combination of both methods, injecting acid at high enough pressure to fracture the formation.

Other well stimulation methods include shock chlorination, explosives, injecting gaseous or solid CO₂, shooting, string shots, perforation, marble shots, sand jetting and large volume injection treatments.

What is needed in the art is a method for stimulating wells, such as water- or hydrocarbon-producing wells that is simple, does not require specialized equipment, does not use chemicals and does not result in the need to dispose of fill removed from the well.

SUMMARY

Described herein is a method of improving the flow of fluids into or along a deviated wellbore that has a partial or complete obstruction caused by fill particles, comprising removing the fill particles from the obstruction and depositing the fill particles within the wellbore, uphole and/or downhole of the partial or complete obstruction.

In one aspect, disclosed herein is a method of removing a partial or complete obstruction in a deviated wellbore, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, comprising:

a) deploying a temporary tubular into the wellbore while circulating a displacement fluid down the bore of the temporary tubular and up an annulus between the temporary tubular and an edge of the wellbore; b) positioning an end of the temporary tubular near the partial or complete obstruction thereby entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the wellbore uphole and/or downhole of the partial or complete obstruction, to thereby restore the flow of fluids into or along the wellbore.

In one embodiment, if the wellbore is partially obstructed, the step of positioning the end of the temporary tubular near the obstruction further comprises positioning the end of the temporary tubular distal to the obstruction.

In one embodiment, if the wellbore is completely obstructed, the step of positioning the end of the temporary tubular near the obstruction comprises:

a) positioning the end of the temporary tubular proximal to the complete obstruction; and b) depositing the entrained fill particles uphole of the obstruction and within the wellbore; and the displacement fluid is circulated from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables flow of fluid past the obstruction or that enables the end of the temporary tubular to be positioned distal to the obstruction.

The method may further comprise, while circulating the displacement fluid from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore, moving the end of the temporary tubular closer to the complete obstruction as fill particles are entrained in the displacement fluid

In some embodiments, after the end of the temporary tubular is positioned distal to the obstruction, the method further comprises:

a) moving the end of the temporary tubular uphole while circulating the displacement fluid down the bore of the temporary tubular and up the annulus between the temporary tubing and the edge of the wellbore; b) entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the wellbore.

In some embodiments of this method the fill particles are deposited uphole of the end of the temporary tubular as the tubular is moving uphole.

In some embodiments the displacement fluid is delivered into the wellbore using a nozzle disposed at the end of the temporary tubular.

In some embodiments the depositing of the entrained fill particles is monitored with a camera, preferably in real time. The camera may be disposed at the end of the nozzle.

The removing of the partial or complete obstruction by the method described herein may stimulate the well to produce fluid, such as water, a hydrocarbon a gas or mixtures thereof.

In some embodiments, the displacement fluid includes a compound that renders the surface of the fill particles hydrophobic.

In some embodiments the method further comprises deposition of the entrained fill particles in a region of the wellbore in which the angle of deviation is greater than about 60°.

In some embodiments computational fluid dynamics is used to select an optimum run in hole rate, pull out of hole rate, and/or fluid flow rate, to ensure that substantially all of the fill particles in the obstruction remain within the wellbore.

In another aspect, described herein is a method of improving the flow of fluids into or along a deviated wellbore that has a partial or complete obstruction caused by fill particles, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, comprising removing the fill particles from the obstruction and depositing the fill particles within the wellbore, uphole and/or downhole of the partial or complete obstruction.

In one embodiment the end of a temporary tubular is positioned near the partial or complete obstruction, and a displacement fluid is circulated out of the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore, to entrain the fill particles in the fluid, remove the fill particles from the obstruction and deposit the fill particles within the wellbore uphole and/or downhole of the partial or complete obstruction.

In one embodiment the fill particles are deposited uphole of the partial or complete obstruction.

In one embodiment the wellbore has a partial obstruction, and the method further comprises positioning the end of the temporary tubular distal to the obstruction.

In one embodiment the wellbore has a complete obstruction, and the method further comprises circulating the displacement fluid out of the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables the end of the temporary tubular to be positioned distal to the obstruction.

In one embodiment the method further comprises, after positioning the end of the temporary tubular distal to the obstruction, withdrawing the end of the temporary tubular uphole while the displacement fluid is circulated out of the end of the temporary tubular, to further entrain fill particles and deposit the particles uphole or downhole of the obstruction.

In one embodiment the method further comprises deposition of the entrained fill particles in a region of the wellbore in which the angle of deviation is greater than about 60°.

In one embodiment computational fluid dynamics is used to select an optimum run in hole rate, pull out of hole rate, and/or fluid flow rate to ensure that substantially all of the fill particles in the obstruction remain within the wellbore.

In another aspect, described herein is a method of removing a partial or complete obstruction in a horizontal wellbore, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, said horizontal wellbore comprising a heel, a first section uphole of the heel and a second section downhole of the heel, comprising:

a) deploying a temporary tubular into the wellbore while circulating a displacement fluid down the bore of the temporary tubular and up an annulus between the temporary tubular and an edge of the wellbore; b) positioning an end of the temporary tubular near the obstruction thereby entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the second section of the wellbore uphole and/or downhole of the obstruction.

In one embodiment the wellbore has a partial obstruction, and the step of positioning the end of the temporary tubular near the obstruction further comprises positioning the end of the temporary tubular distal to the obstruction.

In one embodiment the wellbore has a complete obstruction, and the step of positioning the end of the temporary tubular near the obstruction comprises:

a) positioning the end of the temporary tubular proximal to the complete obstruction; and b) depositing the entrained fill particles uphole of the obstruction; and the displacement fluid is circulated from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables flow of fluid past the obstruction or that enables the end of the temporary tubular to be positioned distal to the obstruction.

In one embodiment the method further comprises, while pulling out of hole (POOH), selecting a POOH rate and/or a fluid flow rate the causes the entrained fill particles to deposit in the wellbore before the heel.

In one embodiment the method further comprises using computational fluid dynamics to select an optimum run in hole rate, POOH rate and/or fluid flow rate, to ensure that substantially all of the fill particles in the obstruction remain within the wellbore.

In one embodiment the method further comprises monitoring the depositing of the entrained fill particles with a camera, optionally in real time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, B and C show an embodiment of the method, performed to eliminate an obstruction that is created by fill in the wellbore and which blocks the flow of fluids along the wellbore. According to the method described herein, the fill particles creating the obstruction are dispersed along the wellbore.

FIGS. 2A and B show an embodiment of the method, used to reduce a beach (secondary obstruction) that is created by deposited fill that accumulates along the wellbore while practicing the method. The secondary obstruction impairs the flow of displacement fluid out of the wellbore. According to this embodiment, the fill particles that create the beach are further dispersed uphole.

FIGS. 3A, B and C show an embodiment of the method, performed to eliminate a partial obstruction that is created by fill in the wellbore and which impairs the flow of fluids along the wellbore. The fill particles creating the partial obstruction are dispersed uphole in the wellbore to a part of the wellbore that has greater diameter and that therefore can better accommodate the particles without impairing flow of fluids along the wellbore.

FIGS. 4A, B and C show an embodiment of the method, performed to eliminate an obstruction that is created by fill in the wellbore and which impairs the flow of fluids into the wellbore due to sediment-clogged rock fissures. The fill particles creating the obstruction are dispersed uphole and downhole in the wellbore away from the fissures, and therefore do not interfere with the flow of fluids into the wellbore.

FIGS. 5A and B show an embodiment of the method, performed to eliminate an obstruction that is created by fill in a wellbore that has a deviation angle of less than 60°, and which blocks the flow of fluids along the wellbore. The fill particles creating the obstruction are dispersed at the bottom of the wellbore.

DETAILED DESCRIPTION

Described herein is a method for removing partial or complete obstructions in deviated wells, and/or for stimulating deviated wells. A deviated well is a well that is not perfectly vertical, or that is purposely deviated from the vertical using controlled angles to reach a location other than directly below the surface location. Examples of a deviated well are horizontal wells and slant wells.

The wellbore is an operational well, that is, a well in an aquifer for producing water, or an injection well or a production well in a geological stratum, for producing hydrocarbons. The wellbore may have production tubing/lining, casing, or it may be an openhole wellbore. The method uses the delivery of a dispersion fluid into the wellbore via a temporary conduit such as a tube, and accordingly, the annulus between the temporary conduit and the edge of the wellbore may comprise on one side the temporary conduit, and on the other side production tubing/lining, casing or other type of tubular conduit, or the wall of the wellbore itself.

The method described herein is designed to disrupt an obstruction or blockage caused by fill in a wellbore, be it an obstruction that prevents the flow of fluid along the wellbore (FIGS. 1A-C and 2A,B), an obstruction that impairs the flow of fluid along the wellbore (FIG. 3A-C), or an obstruction that prevents or impairs the flow of fluid into the wellbore (FIG. 4A-C).

In this method, rather than removing the fill from the wellbore, the fill is moved within the wellbore, to another location in the wellbore that is removed from the location of the obstruction, and where it does not substantially interfere with the flow of fluid along or into the wellbore.

Wellbores can be cleaned to remove fill, such as by using a jet pump to remove debris laden fluids, or swab cups or a reverse circulation junk basket to bail debris out of the wellbore. When a wellbore is cleaned, that is, when fill is removed from the wellbore, it is necessary to dispose of the removed fill. Often this fill is chemically toxic or radioactive, and finding a way to dispose of or store the material is difficult and expensive. The method described herein removes obstructions and/or stimulates a well in which the productivity has been impaired by the presence of fill in the wellbore, and this is accomplished without removing the fill from the wellbore, that is, without transporting the fill to the surface. Thus, the method described herein removes obstructions and/or stimulates the well but avoids the need to dispose of or otherwise handle the fill, providing costs savings in surface processing and disposal of the fill. Instead of removing the fill, the fill is repositioned within the wellbore that is, moved to a location within the wellbore where it no longer impedes production. The location within the wellbore can be a location where the wellbore is wider, a low well area, or an area that is not adjacent to the production zone perforations in the wellbore, an abandoned leg fluidly connected to the wellbore, or it can simply be a dispersion of the accumulated fill along the wellbore.

The method described herein is practiced in a deviated, not vertical, wellbore in which the flow of fluid along the wellbore, or the flow of fluid into the wellbore, is obstructed or impaired by the presence of fill in the wellbore. “Fill”, as used herein means particulate solids, such as sand, silt, residual proppants, and other debris, that is deposited along a wellbore.

According to the method described herein, partial or complete obstructions in a deviated wellbore are treated by inserting a temporary conduit (e.g., coiled tubing) into the wellbore and injecting a displacement fluid from the conduit into the wellbore. As the displacement fluid exits the end of the conduit, it can disturb and entrain the particles in fill that are to be moved from one location in the wellbore to another location within the wellbore. To accomplish this, the end of the temporary conduit is positioned near the obstruction that is to be removed, such that the displacement fluid from the temporary conduit draws in and transports (“entrains”) the fill particles in the obstruction with it, as the fluid flows within the wellbore. In some embodiments the fill particles are displaced uphole of obstruction but still within the wellbore, being carried there by the displacement fluid until the point where the fluid flow rate is insufficient to keep the particles suspended and they settle out of the fluid and are thereby deposited in the wellbore. In some embodiments the fill particles are displaced downhole of obstruction, being carried there by the displacement fluid until the point where the fluid flow rate is insufficient to keep the particles suspended and they settle out of the fluid and are thereby deposited in the wellbore. The injection of fluid into the wellbore via the temporary conduit can continue until the desired amount of fill particles has been repositioned elsewhere in the wellbore.

After this, the temporary conduit may be removed from the wellbore (pulled out of hole—POOH) at a rate and fluid flow rate that ensures that at least some of the fill particles that are to be repositioned are continuously entrained in the fluid and repositioned in the wellbore. The rate of flow of the displacement fluid from the temporary conduit, and the rate of withdrawal of the temporary conduit from the wellbore are slow enough to ensure that substantially all of the fill particles in the partial or complete obstruction remain within the wellbore. In some embodiments about 10-25%, about 20-35%, about 30 to 45%, or less than about 20%, 25%, 35% or 45% of the fill particles in the obstruction are removed from the wellbore. Or in other words, in some embodiments about 75 to 90%, about 65 to 80%, about 55 to 70%, or more than about 80%, 75%, 65% or 55% of the fill particles in the partial or complete obstruction remain in the wellbore.

In the case where the wellbore is only partially obstructed by the fill, the temporary conduit may be disposed on the distal side (downhole) of the obstruction at the beginning of the method described herein (e.g., see FIGS. 3A-C and 4A-C). However, in other cases the wellbore is completely obstructed by the fill, or is obstructed to an extent that the temporary conduit cannot initially be disposed on the distal side of the obstruction. In these cases the fill particles in the obstruction must first be at least partially displaced in order that the temporary conduit may be disposed on the distal side of the obstruction (e.g., FIGS. 1A-C and 2A,B). To accomplish this the method contemplates inserting the temporary conduit downhole to the location of the obstruction, and entraining fill particles on the proximal side of the obstruction in the displacement fluid. The fill particles are deposited uphole of the obstruction, and then the temporary conduit is moved forward (downhole) to further entrain fill particles on the proximal side of the obstruction and deposit them uphole. Eventually, the obstruction will be decreased in size to such an extent that the temporary conduit can be disposed distal to it (downhole of the obstruction) and displacement fluid can then be used to further entrain fill particles and move them uphole or downhole, followed by a removal of the temporary conduit from the wellbore at a POOH rate that further distributes fill particles along the wellbore, as described above.

By eliminating partial or complete obstructions in the wellbore and the tortuous path(s) associated therewith, the producing aquifer or geological stratum will be stimulated to accept or discharge increased quantities of fluid.

FIGS. 1A to C show an embodiment of the method described herein in a cased deviated wellbore that has been perforated along its length (perforations not shown). FIG. 1A shows the wellbore before the method described herein has been performed to remove the obstruction. FIG. 1B shows the wellbore while the method described herein is being performed. FIG. 1C shows the wellbore after the method described herein has been performed, and the obstruction has been removed by moving the fill particles 16 and depositing them along the wellbore.

FIGS. 1 A to C show a horizontal wellbore 10 in production zone 12 lined with a casing 14 and further comprising fill particles 16, which form a complete obstruction that prevents the flow originating from below the obstruction, out of the wellbore. A temporary conduit or tubular 18 such as coiled tubing (“CT”) is disposed into the wellbore until it nears the proximal side of the obstruction (FIG. 1B) at location “A”. A displacement fluid (represented by the arrows) is pumped down the bore of the temporary tubular 18 and exits at the end of the temporary tubular, where it begins to erode the obstruction by disturbing the fill particles therein and entraining them in the fluid. The entrained particles are carried up the bore of the wellbore with the displacement fluid, via the annulus between the temporary tubular and the edge of the wellbore, or they may be deposited downhole as well. Because the pressure of the displacement fluid moving up the annulus is insufficient to transport the particles out of the wellbore, the particles are deposited in the wellbore. After the repositioned particles are deposited in the wellbore, the displacement fluid continues out of the wellbore via the annulus between the temporary tubular and the edge of wellbore. Displacement fluid is pumped through the temporary tubular, and the temporary tubular may be moved forward (downhole) until the end of the temporary tubular has passed beyond and is distal to the obstruction, as shown by the hatched tubular shown at location “B” in FIG. 1B. The operator then begins the process of withdrawing the temporary tubular out of the wellbore. As the tubular is drawn out of the wellbore, fill particles are further disturbed and distributed along the wellbore uphole and downhole of the end of the tubular. The rate of withdrawal of the tubular and the rate of displacement fluid flow from the tubular are selected to optimize the redistribution of the fill particles while ensuring that substantially none of the particles are transported out of the wellbore. For example, typically to perform a wellbore cleanout, in which fill particles are removed from a wellbore, the pump rate for a 2⅜″ coil is about 200 L/min @ 30-40 mPa. The method described herein uses a pump rate, at a given pressure, which is lower than the rate that would be used to remove fill from the wellbore given the conditions of that wellbore, thereby ensuring that the fill particles are repositioned within the wellbore, but not removed from it.

If there is a significant amount of debris at the obstruction, the fill particles that are moved uphole by the displacement fluid may accumulate to the extent that they themselves impair the flow of the displacement fluid out of the wellbore, by forming a beach 17 as shown in FIG. 2A. As a consequence of this accumulation, the ability of the displacement fluid to disturb and redistribute the fill particles may be compromised. To remediate this, the temporary tubular may be withdrawn uphole and towards the beach 17, whereupon the displacement fluid will entrain these particles and may carry them further up the wellbore where they will settle out (deposit). Thus, the accumulated particles deposited as a result of a first sweep are deposited even further uphole of the accumulation by this remedial action. The temporary tubular is withdrawn until the desired flow rate of the displacement fluid is restored, and is then reinserted back down the wellbore towards the obstruction. It may be necessary to perform a number of these “back and forth” maneuvers before the end of the temporary tubular is able to be inserted through the obstruction to the distal side thereof.

FIGS. 3A to C show an embodiment of the method described herein used in an openhole wellbore where the diameter of the wellbore can vary along its length. FIG. 3A shows the wellbore before the method described herein has been performed to remove the obstruction. FIG. 3B shows the wellbore while the method described herein is being performed. FIG. 3C shows the wellbore after the method described herein has been performed and the obstruction has been removed.

Shown is a horizontal wellbore 10 in a production zone 12, the wellbore having a greater diameter at its heel than along its horizontal length. A layer of fill 16 is disposed in the bore of the wellbore, and because the wellbore has differing diameters along its length, the fill forms a partial obstruction at position A, thereby narrowing the opening as shown by the arrows 20. In this embodiment of the method a temporary conduit or tubular 18 is disposed into the wellbore distal to the partial obstruction at A. A displacement fluid (represented by the arrows) is pumped down the bore of the temporary tubular 18 and exits at the end of the tubular. Upon exiting the temporary tubular, the displacement fluid entrains some of the fill particles, which can therefore be moved up the bore of the wellbore with the fluid, in the annulus between the tubing and the edge of the wellbore. The particles fall out of suspension and are deposited along the wellbore before the displacement fluid exits the wellbore. Displacement fluid is pumped through the temporary tubular until the desired widening of the wellbore at location A is achieved (see arrow 20 in FIG. 3C), at which time the operator withdraws the temporary tubular out of the wellbore, at a speed and rate of fluid flow that further disturbs and distributes the solids along the wellbore uphole of the end of the tubular. In the embodiment shown in FIGS. 3A to C, the particles are moved to a wider part of the wellbore where they will not further obstruct the flow of fluids out of the wellbore.

FIGS. 4A to C show an embodiment of the method described herein in a deviated wellbore that comprises a casing that has been perforated at the production zone. FIG. 4A shows the wellbore before the method described herein has been performed to stimulate the well. FIG. 4B shows the wellbore while the method described herein is being performed. FIG. 4C shows the wellbore after the method described herein has been performed and the well has been stimulated.

Shown is a deviated wellbore 10 that comprises a casing 14 that has been perforated 22 at the production zone 12. The wellbore comprises a layer of fill 16 disposed in the bore of the wellbore and covering the lower perforations 22 at the production zone, thus forming an obstruction that reduces fluid flow from the production zone into the wellbore. A temporary conduit or tubular 18 is disposed into the wellbore and moved down the wellbore towards the obstruction. A displacement fluid (represented by the arrows) is pumped down the bore of the temporary tubular 18 and exits at the end of the tubular. Upon exiting the temporary tubular, the displacement fluid disturbs and entrains some of the particles in the fill that covers the perforations, which are therefore moved up or down the bore of the wellbore. At some point the particles fall out of suspension and are deposited along the wellbore. The displacement fluid circulates out of the wellbore through the annulus between the temporary tubular and the edge of wellbore. The temporary tubular may then be positioned distal to the obstruction and pulled out of the hole while running displacement fluid through the tubular, to further entrain fill particles and move them uphole. A camera disposed at the end of the temporary tubular may be used to monitor the redistribution of the fill particles to ensure that the lower perforations 22 are cleared of fill particles. In the embodiment shown in FIGS. 4A to C, the fill is moved uphole and downhole in the wellbore to locations where it will not further cover the perforations in the casing and thereby impede production.

A deviated wellbore may comprise a portion, and sometimes more than one portion, in which the deviation angle, or angle from vertical, is about 60° or less, 0° being a vertical wellbore and 90° being a horizontal wellbore. Commonly, for example, horizontal wells begin with a vertical or near vertical portion and then transition into a horizontal portion, through a section referred to as the “heel”.

Wellbores in which the angle of deviation is less than about 60° or less provide particular problems for transport of particulates therethrough. When the particles entrained therein settle in this portion of the well, they will settle and rather than remaining at that place in the wellbore, they tend to roll to the bottom of the wellbore, or slump, to create a beach that can partially or completely obstruct flow of fluid through the wellbore. Accordingly, in the method described herein, to avoid the formation of a beach, any fill particles that reach a portion of the wellbore wherein the deviation angle is less than 60° are not permitted to settle. Thus, the method described herein avoids the deposition of particles in a region of the wellbore in which the deviation angle is less than 60°, unless that region of the wellbore is at the bottom of the wellbore and below any producing zones.

As discussed above, the method described herein provides that substantially all of the fill particles in the partial or complete obstruction remain within the wellbore. In some embodiments about 75 to 90%, about 65 to 80%, about 55 to 90%, or more than about 80%, 75%, 65% or 55% of the fill particles in the partial or complete obstruction remain in the wellbore. It follows therefore, that in approaching the heel of a wellbore the method contemplates ensuring that substantially all of the fill particles, or in some embodiments, about 75 to 90%, about 65 to 80%, about 55 to 90%, or more than about 80%, 75%, 65% or 55% of the fill particles have settled out of the displacement fluid, and have already been deposited in the wellbore, for if not, they will need to be transported to surface.

This deposition may be accomplished, for example, by increasing the POOH rate above a critical value as the temporary tubular approaches the heel, or by slowing down the rate of flow of the displacement fluid into the wellbore, or by some other means, for example changing the carrying fluid's properties. The critical POOH rate is a POOH rate above which fill will be deposited in the wellbore. This critical POOH rate is a function of wellbore/completion geometry/deviation, circulated fluid type and rate, properties of the fill and the size of the temporary tubular. A higher POOH rate above the critical value results in more fill being deposited in the hole. Any particles that remain in the displacement fluid after the heel has been reached, will have to be removed from the wellbore. Accordingly, the method contemplates controlling a POOH rate and/or a rate of fluid flow, or otherwise modifying the method, to ensure that substantially all of the fill particles in the partial or complete obstruction, or in some embodiments about 75 to 90%, about 65 to 80%, about 55 to 90%, or more than about 80%, 75%, 65% or 55% of the fill particles in the partial or complete obstruction settle out and deposit in the wellbore before the heel is reached.

FIGS. 5A and B show an embodiment of the method described herein in a deviated wellbore that has a deviation angle of less than 60°. FIG. 5A shows the wellbore before the method described herein has been performed, and FIG. 5B shows the wellbore after the method described herein has been performed and the well has been stimulated.

Shown in FIG. 5A is a deviated wellbore 10 that comprises a casing 14 that has been perforated 22 at the production zone 12, and further comprising fill particles 16, which form a complete obstruction that prevents the flow originating from below the obstruction, out of the wellbore. A temporary tubular 18 is disposed into the wellbore until it nears the proximal side of the obstruction and a displacement fluid is pumped down the bore of the temporary tubular 18 and exits at the end of the temporary tubular, where it begins to erode the obstruction by disturbing the fill particles therein and entraining them in the fluid. The entrained particles may be carried up the bore of the wellbore with the displacement fluid, via the annulus between the temporary tubular and the edge of the wellbore, or they may be deposited downhole, or both. Because the pressure of the displacement fluid moving up the annulus is insufficient to transport the particles out of the wellbore, the particles are deposited in the wellbore, either uphole or downhole of the obstruction.

As shown in FIG. 5B, because the deviation angle is less than 60° the particles that fall out of suspension in the portion of the deviated wellbore that has a deviation angle of less than 60° are deposited at the bottom of the wellbore and may accumulate therein blocking the wellbore. If this region of fill deposition and blockage is not above any producing zones, as shown in FIG. 5B, then it will not impede production. Alternatively, if the region of the wellbore having a deviation angle of less than 60° is uphole of another producing zone, then the fill will have to be deposited uphole or downhole of this region, to a region of the wellbore that has a deviation angle of greater than 60°.

Computational fluid dynamics (CFD) modeling is an accurate and powerful tool that can be used to implement the method described herein. To the inventor's knowledge, it is not known to model a method in which the objective is to remove a partial or complete obstruction in a wellbore that is created by the deposition of fill, by displacing the fill elsewhere within the wellbore, rather than by removing the fill from the wellbore.

In accordance with the method described herein, software can accurately predict the optimal fluid flows given a certain set of well parameters such as: borehole parameters (well geometry and deviation, completion geometry), fill parameters (particle size, shape, density, compactness and volume) and production parameters (whether borehole is overbalanced, underbalanced or balanced; pressure and temperature). Other parameters relevant to CFD modeling are equipment parameters such as temporary tubing size, nozzle type in the bottom hole assembly, type of displacement fluid(s) (fluids density, viscosity and other rheology parameters) and jetting pressure. Modeling can predict the flow regimens, velocities and pressures at all points along the wellbore. In combination with real-time data, operators can quickly recognize changing or unforeseen conditions in the well, and the method parameters can be altered in accordance with these conditions, ensuring continued safe and efficient operations.

The combination of parameters discussed above may be used to determine or select, by CFD modeling, the optimum run-in-hole (RIH) rate, pulling out of hole (POOH) rate, pump rates and composition of the displacement fluid, with the objective of ensuring that a partial or complete obstruction in a wellbore that is created by the deposition of fill, is removed by displacing the fill elsewhere within the wellbore, rather than by removing the fill from the wellbore.

The displacement fluid can be, for example, a viscous gel pill with a time delay breaker (that would decrease the viscosity at the end of the treatment), water, hydrocarbons, nitrogen gas, carbon dioxide, acids, oxidizers, surfactants, foams or some combination thereof. Preferably the displacement fluid includes therein a compound that renders the surface of particulates hydrophobic, for example as described in U.S. Pat. No. 7,723,274 and U.S. Pat. No. 8,105,986 to Zhang, or in SPE 171285 (included in FlowRider™), which are incorporated herein by reference. One such exemplary compound for use in the displacement fluid is an organo-siloxane, as described in U.S. Pat. No. 7,723,274.

The type and quantity of fill as well as the wellbore conditions will dictate the composition of the displacement fluid. As is known, the rate at which a particle will fall out of fluid depends on its size, shape and density, and the density and viscosity of the fluid in which the particle is suspended. Bigger particles generally fall faster than smaller particles, and viscous fluids hinder settling. When the flow rate is less than a critical flow rate, particles will fall out of suspension. Accordingly, the critical flow rate of the fluid is controlled to promote particle distribution along the wellbore, to promote settling of the particles out of solution before the heel of the wellbore is reached, or to otherwise avoid the deposition of particles in a region of the wellbore in which the deviation angle is less than 60°. The angle of deviation has little effect on the critical flow rate if the angle is greater than 60°, however, if less than 60° it does affect the critical flow rate.

Coiled tubing and a cement and acid pumper, and/or a nitrogen pump may be used to administer these fluids to the well, using methods that are known in the art. The coiled tubing may comprise at its end a wash nozzle, such as a wash nozzle available from National Oilwell Varco.

A camera may be placed at or near the end of the coiled tubing, in order to monitor the progress of the removal of the partial or complete obstruction and the displacement of the fill particles within the wellbore. Preferably the camera will provide real-time information while the removal of the partial or complete obstruction and the displacement of the fill particles within the wellbore is ongoing.

While the method has been described in conjunction with the disclosed embodiments and examples which are set forth in detail, it should be understood that this is by illustration only and the method is not intended to be limited to these embodiments and examples. On the contrary, this disclosure is intended to cover alternatives, modifications, and equivalents which will become apparent to those skilled in the art in view of this disclosure. 

1. A method of removing a partial or complete obstruction in a deviated wellbore, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, comprising: a) deploying a temporary tubular into the wellbore while circulating a displacement fluid down the bore of the temporary tubular and up an annulus between the temporary tubular and an edge of the wellbore; b) positioning an end of the temporary tubular near the partial or complete obstruction thereby entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the wellbore uphole and/or downhole of the partial or complete obstruction, to thereby restore the flow of fluids into or along the wellbore.
 2. The method of claim 1 in which the wellbore is partially obstructed, and the step of positioning the end of the temporary tubular near the obstruction further comprises positioning the end of the temporary tubular distal to the obstruction.
 3. The method of claim 1 in which the wellbore is completely obstructed, and the step of positioning the end of the temporary tubular near the obstruction comprises: a) positioning the end of the temporary tubular proximal to the complete obstruction; and b) depositing the entrained fill particles uphole of the obstruction and within the wellbore; and the displacement fluid is circulated from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables flow of fluid past the obstruction or that enables the end of the temporary tubular to be positioned distal to the obstruction.
 4. The method of claim 4 further comprising, while circulating the displacement fluid from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore at step (c), moving the end of the temporary tubular closer to the complete obstruction as fill particles are entrained in the displacement fluid.
 5. The method of claim 4 further comprising positioning the end of the temporary tubular distal to the obstruction.
 6. The method of claim 2 further comprising, after the end of the temporary tubular is positioned distal to the obstruction: a) moving the end of the temporary tubular uphole while circulating the displacement fluid down the bore of the temporary tubular and up the annulus between the temporary tubing and the edge of the wellbore; b) entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the wellbore.
 7. The method of claim 5 further comprising, after the end of the temporary tubular is positioned distal to the obstruction: a) moving the end of the temporary tubular uphole while circulating the displacement fluid down the bore of the temporary tubular and up the annulus between the temporary tubing and the edge of the wellbore; b) entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the wellbore.
 8. The method of claim 6 wherein the fill particles are deposited uphole of the end of the temporary tubular as the tubular is moving uphole.
 9. The method of claim 7 wherein the fill particles are deposited uphole of the end of the temporary tubular as the tubular is moving uphole.
 10. The method of claim 1 further comprising delivering the displacement fluid into the wellbore using a nozzle disposed at the end of the temporary tubular.
 11. The method of claim 1 further comprising monitoring the depositing of the entrained fill particles with a camera.
 12. The method of claim 11 further comprising monitoring the depositing of the entrained fill particles in real time, with the camera.
 13. The method of claim 11 wherein the camera is disposed at the end of the nozzle.
 14. The method of claim 1 wherein the removing of the partial or complete obstruction stimulates the well to produce fluid.
 15. The method of claim 14 wherein the fluid comprises water, a hydrocarbon, a gas or mixtures thereof.
 16. The method of claim 15 wherein the gas is nitrogen, carbon dioxide, natural gas, air or propane.
 17. The method of claim 1 wherein the displacement fluid includes a compound that renders the surface of the fill particles hydrophobic.
 18. The method of claim 1 further comprising deposition of the entrained fill particles in a region of the wellbore in which the angle of deviation is greater than about 60°.
 19. The method of claim 1 comprising using computational fluid dynamics to select an optimum run in hole (RIH) rate, a pull out of hole (POOH) rate and/or a fluid flow rate.
 20. A method of improving the flow of fluids into or along a deviated wellbore that has a partial or complete obstruction caused by fill particles, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, comprising removing the fill particles from the obstruction and depositing the fill particles within the wellbore, uphole and/or downhole of the obstruction.
 21. The method of claim 20 wherein an end of a temporary tubular is positioned near the obstruction, and a displacement fluid is circulated out of the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore, to entrain the fill particles in the fluid, remove the fill particles from the obstruction and deposit the fill particles within the wellbore uphole and/or downhole of the obstruction.
 22. The method of claim 20 wherein the fill particles are deposited uphole of the obstruction.
 23. The method of claim 20 in which the wellbore has a partial obstruction, further comprising positioning the end of the temporary tubular distal to the obstruction.
 24. The method of claim 20 in which the wellbore has a complete obstruction, further comprising circulating the displacement fluid out of the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables the end of the temporary tubular to be positioned distal to the obstruction.
 25. The method of claim 21 further comprising withdrawing the end of the temporary tubular uphole while the displacement fluid is circulated out of the end of the temporary tubular, to further entrain fill particles and deposit the particles uphole or downhole of the obstruction.
 26. The method of claim 20 further comprising deposition of the entrained fill particles in a region of the wellbore in which the angle of deviation is greater than about 60°.
 27. The method of claim 20 further comprising using computational fluid dynamics to select an optimum run in hole (RIH) rate, pull out of hole (POOH) rate and/or fluid flow rate.
 28. A method of removing a partial or complete obstruction in a horizontal wellbore, said obstruction being created by fill particles and obstructing the flow of fluids into or along the wellbore, said horizontal wellbore comprising a heel, a first section uphole of the heel and a second section downhole of the heel, comprising: a) deploying a temporary tubular into the wellbore while circulating a displacement fluid down the bore of the temporary tubular and up an annulus between the temporary tubular and an edge of the wellbore; b) positioning an end of the temporary tubular near the obstruction thereby entraining the fill particles in the displacement fluid; and c) depositing the entrained fill particles within the second section of the wellbore uphole and/or downhole of the obstruction.
 29. The method of claim 28 in which the wellbore has a partial obstruction, and the step of positioning the end of the temporary tubular near the obstruction further comprises positioning the end of the temporary tubular distal to the obstruction.
 30. The method of claim 28 in which the wellbore has a complete obstruction, and the step of positioning the end of the temporary tubular near the obstruction comprises: a) positioning the end of the temporary tubular proximal to the complete obstruction; and b) depositing the entrained fill particles uphole of the obstruction; and the displacement fluid is circulated from the end of the temporary tubular and up the annulus between the temporary tubular and the edge of the wellbore until an amount of fill particles is removed from the obstruction that enables flow of fluid past the obstruction or that enables the end of the temporary tubular to be positioned distal to the obstruction.
 31. The method of claim 28 further comprising, while pulling out of hole (POOH), selecting a POOH rate and/or a fluid flow rate the causes the entrained fill particles to deposit in the wellbore before the heel.
 32. The method of claim 28 further comprising using computational fluid dynamics to select an optimum run in hole (RIH) rate, POOH rate and/or fluid flow rate.
 33. The method of claim 28 further comprising monitoring the depositing of the entrained fill particles with a camera.
 34. The method of claim 33 further comprising monitoring the depositing of the entrained fill particles in real time, with the camera. 